In the cyclic process for making hydrogen peroxide, alkyl anthraquinones are catalytically hydrogenated in solution to yield the corresponding anthrahydroquinones. Upon oxidizing the anthrahydroquinone, hydrogen peroxide is produced and the alkyl anthraquinone is regenerated. The hydrogen peroxide is then removed from the solution, usually by extraction with water, and the solution containing regenerated alkyl anthraquinone is recycled to the hydrogenation step.
In this process, the conventional catalytic metals have been Raney nickel and the noble metals, platinum, rhodium and palladium, of which the last has been preferred because of its resistance to poisoning and its ease of regeneration. In this regard, it was disclosed by Sprauer in U.S. Pat. No. 2,657,980 that life and activity of palladium catalysts are extended by supporting them on activated alumina, particularly, alpha- or gamma-alumina. In addition, Keith et al disclose in U.S. Pat. No. 3,635,841 that palladium catalysts supported on delta-alumina, theta-alumina or mixtures thereof free of alpha- or gamma-alumina are effective. Both fixed bed and fluid bed (slurry) operations have been used for these catalysts.